The subject matter disclosed herein relates to a method and device for inspection of an asset (e.g., blades of a turbine engine).
Video inspection devices (or optical devices), such as video endoscopes or borescopes, can be used to inspect a surface of an object to identify and analyze anomalies (e.g., pits or dents) on the object that may have resulted from, e.g., damage, wear, corrosion, or improper installation. A video inspection device can be used to capture and display a two-dimensional image of the surface of a viewed object showing the anomaly to determine the dimensions of an anomaly on the surface. This two-dimensional image of the surface can be used to generate three-dimensional data of the surface that provides the three-dimensional coordinates (e.g., (x, y, z)) of a plurality of points on the surface.
There are various existing techniques that can be used to provide the three-dimensional coordinates of the surface points in the two-dimensional image (e.g., stereoscopic imaging and structured light methods such as phase shift analysis, phase shift moiré, laser dot projection, etc.). Some of these techniques, including structured light methods, require multiple images (e.g., 3 to 6 images) captured sequentially. In inspecting a rotating object (e.g., turbine blades) rotating past the video inspection device using a structured light method, the rotating object would have to stop to allow the inspector to take the required multiple images, which is not ideal. Stereoscopic imaging can be used to provide the three-dimensional coordinates of the surface points in inspecting these rotating objects since typically a stereo image taken at a single point in time is required with multiple sensors synchronized to each other. Since stereoscopic imaging is dependent upon finding the same points on the surface, surfaces that have minimal texture (e.g., a surface with a ceramic thermal barrier coating) can result in false matching and inaccurate three-dimensional mapping.
In one example, a video inspection device can be used to inspect a turbine blade of an engine on an aircraft or power generation turbine. The video inspection device is typically inserted through a borescope port in the turbine between stationary vanes to inspect the turbine blades of an adjacent stage of rotating turbine blades. While the video inspection device is fixed in position, the core of the turbine is rotated such that the turbine blades pass through the field of view of the video inspection device. It is common for video to be recorded showing the turbine blades passing by. In addition, two-dimensional still images of selected turbine blades (e.g., turbine blades that have anomalies that the inspector notices) may also be captured during the inspection. Since capturing two-dimensional still images of all of the turbine blades requires large amounts of data that is difficult to transmit and manage, an inspection may not capture a two-dimensional image of each turbine blade, preventing an inspection from obtaining three-dimensional data for each turbine blade.
Furthermore, video of the inspection is generally compressed, which can lead to compression artifacts reducing its usefulness for automated analysis. Since the video and still images provide only two-dimensional data, any automated analysis generally relies on color, edge detection, etc. to try to assess turbine blade condition. Furthermore, any automated analysis may also either perform complicated three-dimensional model matching or make assumptions about magnification, optical distortion, etc. in order to quantify the sizes of identified indications since the position of the video inspection device with respect to the turbine blades can vary during and between inspections.